phosphodiesterase

Selectively inhibits cGMP-specific phosphodiesterase type 5. The mechanism of penile erection involves the release of nitric oxide into the corpus cavernosum of the penis during sexual stimulation. Nitrous oxide activates cGMP, which causes smooth muscle relaxation allowing the flow of blood into the corpus cavernosum. Phosphodiesterase type 5 inhibitors prevent the breakdown of cGMP by phosphodiesterase, leading to increased cGMP levels and prolonged smooth muscle relaxation promoting the flow of blood into the corpus cavernosum.

Indications

Treatment of erectile dysfunction in the presence of sexual stimulation

Treatment of pulmonary arterial hypertension

Contraindications and cautions

Contraindicated with allergy to any component of the drugs, for women or children; concurrent use of nitrates or alpha blockers.

Use cautiously with hepatic or renal impairment; with anatomical deformation of the penis; with known cardiac disease (effects of sexual activity need to be evaluat- ed); congenital prolonged QT interval; unstable angina; hypotension (systolic lower than 90); uncontrolled hypertension (higher than 170/110); severe hepatic impair- ment; end-stage renal disease with dialysis; hereditary degenerative retinal disorders.

Adverse effects

CNS: Headache, abnormal vision, changes in color vision, fatigue, hearing loss

CV: Flushing, angina, chest pain, hypertension, hypotension, MI, palpitations, orthostatic hypotension, tachycardia

GI: Dyspepsia, diarrhea, abdominal pain, dry mouth, esophagitis, gastritis, GERD, nausea, abnormal LFT

GU: Abnormal erection, spontaneous erection, priapism

Respiratory: Rhinitis, sinusitis, dyspnea, epistaxis, pharyngitis, nasal congestion

Other: Flulike symptoms, edema, pain, rash, sweating, myalgia

Interactions

Drug-drug

Possible severe hypotension and serious cardiac events if combined with nitrates, alpha blockers; this combination is contraindicated

Possible increased levels and effects if taken with ketoconazole, itraconazole, erythromycin; monitor patient and reduce dosage as needed

Increased serum levels if combined with indinavir, ritonavir; if these drugs are being used, limit dosage

Reduced levels and effectiveness if combined with rifampin

Risk for increased cardiac effects, decreased BP, flushing if combined with alcohol; warn patient of this possibility if alcohol is used Drug-food

Possible increased levels if taken with grapefruit juice

Nursing considerations

Assessment

History: Allergy to any component of the tablet, concurrent use of nitrates or alpha blockers; unstable angina; hypotension; uncontrolled hypertension; severe hepatic impairment; end-stage renal disease with dialysis; hereditary degenerative retinal disorders; anatomical deformation of the penis, cardiac disease, congenital prolonged QT interval

Physical: Orientation, affect; skin color, lesions; R, adventitious sounds; P, BP, ECG, LFTs, renal function tests

Interventions

Assure diagnosis of erectile dysfunction and determine underlying causes and other appropriate treatment.

Advise patient that drug does not work in the absence of sexual stimulation. Limit use to once per day.

Remind patient that drug does not protect against STDs and that appropriate meas- ures should be taken.

Black box

warning Advise patient to never take this drug with nitrates or alpha blockers; serious and even fatal complications can occur.

Warn patient of the risk of lowered BP and dizziness if taken with alcohol.

Teaching points

Take these drugs before anticipated sexual activity; the drug will stay in your body for up to 4 hours (sildenafil, vardenafil), or up to 36 hours (tadalafil). The drug will have no effect in the absence of sexual stimulation.

These drugs will not protect you from sexually transmitted diseases; use appropriate precautions.

Do not take these drugs if you are taking any nitrates or alpha blockers or other drugs for treating erectile dysfunction; serious side effects and even death can occur.

Many drugs may interact with these drugs; consult your health care provider before taking any drug, including over-the-counter drugs and herbal therapies; dosage adjustments may be needed.

Know that combining these drugs with alcohol could cause dizziness, loss of blood pressure, increased flushing.

You may experience these side effects: Headache, dizziness, upset stomach, runny nose, muscle pains; these side effects should go away within a couple of hours. If side effects persist, consult your health care provider.

Report difficult or painful urination, vision changes, hearing loss, fainting, erection that persists for longer than 4 hours (if this occurs, seek medical assistance as soon as possible).